A reverse passive hemagglutination (RPHA-G) technique for the automated screening of hepatitis B surface antigen (HBsAg) on the Groupamatic 360 (Kontron International, Zürich, Switzerland) has been developed. It is more sensitive than manual RPHA (RPHA-M) and nearly as sensitive as radioimmunoassay (RIA); it detects 6 ng/ml of HBsAg, compared to 3 ng/ml by RIA and 25 ng/ml by RPHA-M. Although it is slightly inferior to the other two methods in respect of specificity, the incidence of false-positive reactions was only 0.34%. The test can also be performed manually without the Groupamatic.